Affect is most often a verb meaning to influence or change something. Effect is most often a noun meaning the result or outcome of a change. The common test is: if you can replace the word with influence, use affect; if you can replace it with result, use effect.

Use affect when one thing influences another, often without being the direct cause of a final outcome. It answers the question What does it change or influence. It commonly appears in academic, medical, business, and everyday contexts when describing impact on mood, behavior, performance, or conditions.

Rule	🇨🇳 中文 Rule	Example	🇨🇳 中文 Example
Use affect for influence on a person or thing	🧠 对一个人或事物的影响使用 affect	Noise can affect concentration.	📝 噪音会影响专注力。
Use affect with measurable impacts	🧠 对可衡量的影响使用 affect	The storm may affect flights.	📝 风暴可能影响航班。
Use affect for changes in feelings or mood	🧠 对情感或情绪的变化使用 affect	The news affected him deeply.	📝 新闻深深地影响了他。

Use effect for the outcome or end result of an action, event, or cause. It answers the question What happened because of it. It commonly appears with verbs like have, produce, see, feel, and with adjectives describing results.

Rule	🇨🇳 中文 Rule	Example	🇨🇳 中文 Example
Use effect for the result of a cause	🧠 用 effect 来表示原因的结果	The effect of the storm was widespread.	📝 风暴的影响范围很广。
Use have an effect on for impact phrased as a noun	🧠 将 have an effect on 用作名词形式的影响	Stress can have an effect on sleep.	📝 压力可能影响睡眠。
Use side effect for secondary results	🧠 使用 side effect 表示次要结果	Drowsiness is a common side effect.	📝 嗜睡是一个常见的副作用。

A practical way to choose is to try a synonym in your sentence. If influence fits, choose affect. If result or outcome fits, choose effect. This method works for most everyday writing and speaking.

Rule	🇨🇳 中文 Rule	Example	🇨🇳 中文 Example
If influence fits, use affect	🧠 如果“影响”（influence）合适，就使用 affect	Heat can affect batteries.	📝 热量会影响电池。
If result fits, use effect	🧠 如果“结果”（result）合适，就使用 effect	The effect was immediate.	📝 结果是即时的。

Certain word partnerships strongly prefer one form. Learning these chunks helps you choose quickly and sound natural. Many of them are fixed phrases used in formal and informal English.

Word/Phrase	🇨🇳 中文 Word/Phrase	Definition	🇨🇳 中文 Definition	Example	🇨🇳 中文 Example
affect the outcome	🧩 affect the outcome	influence the final result	🧩 influence the final result	Small errors can affect the outcome.	🧩 小错误可以影响结果。
have an effect on	🧩 have an effect on	produce an impact on	🧩 produce an impact on	Caffeine has an effect on alertness.	🧩 咖啡因会影响警觉性。
take effect	🧩 take effect	begin to work or apply	🧩 begin to work or apply	The new rule takes effect tomorrow.	🧩 新规则将于明天生效。
in effect	🧩 in effect	currently operating or true	🧩 现行中/当前正在生效	The policy is still in effect.	🧩 政策仍在生效中。
to that effect	🧩 to that effect	expressing something similar	🧩 表示类似意思	She said something to that effect.	🧩 她说了类似的话。

Effect can be a verb meaning to cause something to happen or to bring something about. It is more formal and often used with nouns like change, reform, solution, and improvement. Use it when someone successfully makes a planned result happen, not just influences it.

Rule	🇨🇳 中文 Rule	Example	🇨🇳 中文 Example
Use effect meaning bring about	🧠 使用 effect 意指带来/促成（bring about）	The new CEO effected major changes.	📝 新任CEO推动了重大变革。
Often pairs with nouns like change or reform	🧠 经常与如 change 或 reform 等名词搭配	The policy aims to effect reform.	📝 该政策旨在促成改革。

Affect can be a noun in psychology meaning outward emotional expression, such as facial expression, tone, or visible mood. This meaning is specialized and mostly appears in clinical or academic settings. In everyday English, people usually say mood or emotion instead.

Rule	🇨🇳 中文 Rule	Example	🇨🇳 中文 Example
Use noun affect for observable emotional display	🧠 使用名词 affect 表示可观察到的情感表现	The clinician noted a flat affect.	📝 医师记录了扁平情感。
Prefer mood or emotion in general contexts	🧠 在一般语境中更偏好 mood 或 emotion	His mood seemed low today.	📝 他的情绪今天似乎低落。

Affect emphasizes the process of influence or change, while effect emphasizes the final outcome. If you want to highlight what caused a shift, affect is usually the right choice. If you want to highlight what happened as a consequence, effect is usually the right choice.

In everyday writing, you will mostly use affect as a verb and effect as a noun. The verb effect and the noun affect are correct but less common, so they can sound formal or technical. Choosing the common forms improves clarity unless you specifically need the specialized meaning.

Rule	🇨🇳 中文 Rule	Example	🇨🇳 中文 Example
Default to affect verb and effect noun for clarity	🧠 为了清晰起见，默认使用 affect（动词）和 affect（名词）	Poor lighting affects photos and the effect is noticeable.	📝 光线差会影响照片，效果很明显。
Use effect verb in formal contexts	🧠 在正式场合使用 effect 作为动词	The committee hopes to effect change.	📝 委员会希望推动变革。
Use affect noun in clinical contexts	🧠 在临床语境中使用 affect 作为名词	Restricted affect may indicate depression.	📝 限制性情感可能表示抑郁。